In current practice, it is usual for the operation of driving the engine of a vehicle by means of its starter to be terminated under the control of the driver of the vehicle, who for this purpose releases the ignition key when the engine makes a characteristic sound. However, vehicle engines are tending nowadays to be made more and more quiet, thus making it increasingly difficult for the driver to hear the characteristic sound and therefore more difficult to know when to release the ignition key. As a result, the release of the key tends to be delayed, so that the starter and the engine are subjected to unnecessary, and severe forces.
Numerous control systems for the automatic stopping of the starter are known, which employ an analysis of voltage or current signals to determine when the engine has started, that is to say the instant when it becomes autonomous enough to reach its slow running mode by itself, this being the instant at which the starter is no longer required and should be stopped. In particular, it is known from French patent specification No. FR 2 696 417 to control cut-off of the starter by comparing the battery voltage with a threshold voltage, the starter being cut-off when the voltage of the battery reaches this threshold value. From the point of view of the number of components used and the cost of the components, analysis of the voltage signal is preferred to analysis of the current signal.
However, control of cut-off by comparison with a threshold voltage, such as is described in specification FR 2 696 417, is not fully satisfactory. In particular, the voltage across the battery terminals can vary considerably over time, as a function in particular of its state of maintenance or of the ambient temperature. As a result, if the battery voltage is too low, it can happen that the starter is not stopped immediately after the engine has successfully started, and operates well beyond the time that is actually necessary.
On the other hand, if the battery voltage is too high, it can happen that the starter is cut off too soon, well before the engine has properly started.